The intermediary metabolism of selenium in chick liver will be studied to determine whether inducing agents such as phenobarbital alter either the reduction of Se O3 to H2Se or the methylation of the latter compound to (CH3)2Se and/or (CH3)3Se plus 2. We will also determine whether an inducible demethylation occurs which reduces the excretion of Se from loaded animals thus potentiating its toxicity. Studies will be conducted to localize these events within the cell. We will also seek to determine whether the biochemical basis of protection from nitroaromatic drug and paraquat toxicity is due to a reduction of protein sulfoxidation.